It has been disclosed that certain pyrrolidinone compounds have herbicidal activity. For example, U.S. Pat. Nos. 4,110,105 and 4,210,589 disclose a series of N-(optionally substituted)phenyl 4-haloalkyl pyrrolidinones. These include the commercial herbicide fluorochloridone [(3-chloro-4-chloromethyl-1-(3-trifluoromethylphenyl)-2-pyrrolidinone], employed to control weeds in crops such as winter wheat and sunflower.
U.S. Pat. No. 5,123,954 discloses another series of herbicidal pyrrolidinones, namely N-(substituted)phenyl-3-(substituted) phenyl-4-ethyl pyrrolidinones, and indicates that certain N-(3-isopropylphenyl)-3-(halophenyl)pyrrolidinones of this type are particularly useful as selective herbicides for control of weeds in paddy rice crops.
Some N-benzyl pyrrolidinones are also known in the art. U.S. Pat. Nos. 4,069,038 and 4,119,636 disclose N-(benzyl and p-chlorobenzyl)-3-chloro-4-chloromethyl-2-pyrrolidinones as specific herbicidal compounds and contain a disclosure of a broader generic class of 4-chloro- or bromoalkyl compounds of this type as being herbicidal. U.S. Pat. No. 5,114,466 discloses N-(benzyl or 3-halobenzyl)-3-(chloro or bromo)-4-C.sub.3 -C.sub.5 haloalkyl)pyrrolidinones, again as herbicides particularly useful for controlling weeds in paddy rice.
As a consequence of the presence of unsymmetrically substituted carbon centers in many of the compounds of this type, cis-trans isomers may exist. Varying comments have been made in the above patents concerning the relationship between this isomerism, particularly at the 3- and 4- positions on the pyrrolidinone ring, and the herbicidal activity of the compounds described therein. For instance, U.S. Pat. No. 4,210,589 shows (Table III) that for one compound at least the cis-isomer has much greater herbicidal activity than the trans-isomer. U.S. Pat. No. 5,114,466 (column 4, lines 21-27) indicates a similar preference for cis-isomers. On the other hand, U.S. Pat. No. 5,123,954 indicates a preference for trans-isomers.